1. Field of the Invention
The present invention relates to an image forming method and an apparatus for forming an image on a printing medium by ejecting a liquid from a liquid ejecting head. More particularly, the invention is suitable for application to an ink-jet printer mounting a full-line type ink-jet head, in which a plurality of ejection openings for liquid are arranged over the entire width of an image forming region of the printing medium.
2. Description of the Related Art
An ink-jet printer for forming a desired image by ejecting an ink droplet onto a paper, a cloth, a resin, a metal and the like, features non-contact recording with respect to a printing medium and thus is superior in low noise, high printing speed, capability of high resolution printing, easiness of color printing, and capability of down-sizing of the overall apparatus.
As one of such ink-jet printers, there has been known a printer shown in FIG. 10, in which a plurality of elongated so-called full-line type ink-jet heads, each having a plurality of ejection openings arrayed over the entire width of an image forming region of a printing medium, are arranged in a feeding direction of the printing medium.
Namely, the printer includes four ink cartridges 33Y, 33M, 33C, and 33B respectively storing a yellow ink, a magenta ink, a cyan ink, and a black ink (hereinafter referred to as ink cartridge 33) and four ink-jet heads 21Y, 21M, 21C and 21B (hereinafter referred to as ink-jet head 22) connected to respective ink cartridges 33 via ink supply tubes 32, respectively.
The ink-jet heads 21, each of which is switched power supply between ON and OFF for respective ones of not shown electrothermal transducers by a head driver 61 connected to a control unit 60, are arranged with a predetermined interval along a feeding direction of an endless feeding belt 62 so as to face a platen 63 via the feeding belt 62. By head moving means 64 for recovery process, which is controlled by the control unit 60, the ink-jet heads 21 are moved up and down with respect to the platen 63. On the side portion of each ink-jet head 21, capping members 22, for performing recovery process of the ink-jet heads 21 by performing preliminary ejection of old inks within not shown ink passages provided within the ink-jet heads 21 from the ejection openings in advance of printing operation with respect to a printing paper 65, are arranged in a condition shifted by one-half pitch with respect to an arrangement interval of the ink-jet heads 21. By moving means 66, which is controlled by the control unit 60, the capping members 22 are moved to positions immediately below the ink-jet heads 21 at recovery process positions so as to receive waste inks ejected from the ejection openings.
The feeding belt 62 feeding the printing paper 65 is wound around a driving roller 68 connected to a belt driving motor 67. The driving direction of the feeding belt 62 is switched by a motor driver 69 connected to the control unit 60. On the upstream side of the feeding belt 62, an electrostatic charger 70 is provided for electrostaticly charging the feeding belt 62 for adhering the printing paper 65 on the feeding belt 62. The electrostatic charger 70 is switched ON and OFF by a driver 71 connected to the control unit 60. To a pair of paper feeding rollers 72 for supplying the printing paper 65 on the feeding belt 62, a paper feeding motor 73, for rotatingly driving the pair of paper feeding rollers 72, is connected. The operation of paper feeding motor 73 is switched by a motor driver 74 connected to the control unit 60.
Accordingly, in advance of the printing operation for the printing paper 65, the ink-jet heads 21 are elevated to the recovery process position away from the platen 63. Then, the capping member 22 is moved immediately below the ink-jet heads 21. Then, after the recovery operation for the ink-jet heads 21, the capping member 22 is returned to an initial position. Also, the ink-jet heads 21 are moved toward the platen up to the image forming position. Then, the electrostatic charger 70 is actuated while the feeding belt 62 is driven. Also, the printing paper 65 is mounted on the feeding belt 62 by the paper feeding roller 72, and a desired color image is formed on the printing paper 65 by the ink-jet heads 21.
In the full-line type ink-jet printer shown in FIG. 10, the ink-jet heads 21 are located on the upper side of the ink cartridges 33. A problem of causing leakage of the ink through the ejection openings of the ink-jet heads 21 due to a liquid pressure of the ink stored in the cartridges 33 can be successfully prevented.
Because of the constructions set forth above, when the ink-jet heads 21 are elevated from the image forming position to the recovery process position, as illustrated in a sectional structure of the lower end portion of the ink-jet heads 21 in FIG. 11, an ink surface (ink meniscus) M of the ejection openings 40 is located at a position shown by a two dotted line at the image forming position, namely at an ejection opening surface 44 where the ejection openings 40 are formed, and whereas, at the recovery process position above the image forming position, a waterhead difference between the ink surface M and the ink cartridge 33 becomes large to cause recession of the ink surface M into the ink passage 58, as shown by the solid line.
As a result, foreign matter W, such as dust and the like deposited in the vicinity of the ejection openings 40 can be sucked into the ink passage 58 to be held within the ink passage 58 even if the recovery process is performed. In such case, ejection failure can result to prevent formation of a good quality image.
Such drawback may be caused not only in the ink but also in treatment liquid for adjusting printing ability of the ink on and/or in the printing medium.
An object of the present invention is to provide an image forming method which can successfully prevent the drawback of sucking foreign matter, such as dust or the like from the ejection openings into ink passages even when a liquid ejection head ejecting a liquid is elevated from an image forming position to a recovery process position.
Another object of the present invention is to provide an image forming apparatus which can implement the image forming method set forth above.
The first aspect of the present invention is an image forming method forming an image on a printing medium in an image forming position utilizing a liquid ejection head for forming the image on the printing medium by ejecting liquid in the image forming position, comprising:
a step of performing a recovery process at a recovery process position set on an upper side of the image forming position for recovering ejecting condition of liquid from the liquid ejecting head; and
a step of closing a liquid supply passage for supplying liquid to the liquid ejection head during movement of the liquid ejection head from the image forming position to the recovery process position.
The second aspect of the present invention is an apparatus for forming an image on a printing medium utilizing a liquid ejection head provided with an ejection opening for ejecting liquid, comprising:
a liquid supply passage connected to the liquid ejection head;
recovery process means for recovering ejecting condition of liquid from the liquid ejection head;
head moving means for moving the liquid ejection head between the recovery process position for performing recovery process of the liquid ejection head by the recovery process means and an image forming position for forming an image on the printing medium by the liquid ejection head; and
closing means for closing the liquid supply passage during movement of the liquid ejection head at least to the recovery process position by the head moving means.
According to the present invention, when the image is formed on the printing medium, the liquid ejection head is moved into the image forming position by the head moving means to form the image on the printing medium using the liquid ejection head at the image forming position.
When recovery process of the liquid ejection head is performed, the liquid supply passage is closed by operating the closing means to restrict flow of liquid between the ejection opening of the liquid ejection head and the liquid supply passage. At this condition, after moving the liquid ejection head from the image forming position to the recovery process position by the head moving means, the closure means is again operated to open the liquid supply passage, and recovery process of the liquid ejection head is performed by the recovery process means at the recovery process position.
The liquid ejection head on which the recovery process has been effected is again returned to the image forming position by the head moving means and image formation on the printing medium is performed.
According to the present invention, when the recovery process is performed in order to recover ejecting condition of liquid from the liquid ejection head at the recovery process position set on the upper side of the image forming position, since the liquid supply passage for supplying liquid to the liquid ejection head is closed during movement of the liquid ejection head from the image forming position to the recovery process position, even when the liquid ejection head for ejecting liquid is elevated from the image forming position to the recovery process position, a problem of suction of foreign matter, such as dust or the like into the ink passage from the ejection opening can be successfully prevented.
In the image forming method by the first aspect of the present invention, the recovery process position may include a capping position for covering an ejection opening surface provided with an ejection opening of the liquid ejection head for ejecting liquid, and a wiping position set on an upper side of the capping position for wiping the ejection opening surface.
The recovery process may include at least one of steps of performing preliminary ejection of liquid from the ejection opening of the liquid ejection head at the capping position, expelling liquid from the ejection opening of the liquid ejection head by pressurizing the liquid supply passage, and sucking liquid from the ejection opening of the liquid ejection head.
Liquid may be ink or treatment liquid for adjusting printing ability of the ink on and/or in the printing medium.
In the image forming apparatus by the second aspect of the present invention, the recovery process position may include a capping position and a wiping position located above the capping position, the recovery process means having a capping member for covering the ejection opening surface provided with an ejecting opening of the liquid ejection head ejecting liquid at the capping position and a wiping member for wiping the ejection opening surface at the wiping position. The recovery process means may preliminarily eject liquid from the ejection opening of the liquid ejection head at the capping position, expelling liquid from the ejection opening of the liquid ejection head by actuating the liquid supply means or sucking liquid from the ejection opening of the liquid ejection head via the capping member.
The liquid ejection head may have an ejection energy generating portion for ejecting liquid from the ejection opening. In this case, the ejection energy generating portion may have an electrothermal transducer for generating thermal energy.
The ejection openings may be provided for the liquid ejection head and may be arranged over the entire width of a printing region of the printing medium.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.